The present invention relates to cellular elastomers which are preferably anisotropic without an external influence, in particular even without the action of a man-made magnetic field, with the anisotropy being defined by the compressive modulus, preferably measured by a method based on DIN ISO 7743, in one of 3 orthogonal directions being greater than that in the other two directions by a factor of at least 1.5, preferably a factor of from 2 to 50. The invention further relates to cellular elastomers comprising magnetizable particles which have a chain-like alignment preferably parallel to one another along one spatial direction. In addition, the invention relates to a process for producing cellular elastomers, preferably cellular polyurethane elastomers, particularly preferably cellular polyurethane elastomers having a density in accordance with DIN EN ISO 845 in the range from 200 kg/m3 to 5000 kg/m3, with the density being based on the total weight of the cellular polyurethane elastomer, i.e. including the weight of the magnetizable particles, wherein the cellular elastomers are produced in the presence of magnetizable particles so that these magnetizable particles are present in the cellular elastomer and the production of the cellular elastomers is carried out in the presence of a preferably man-made magnetic field which has a flux density of greater than 0.01 tesla, preferably a flux density in the range from 0.05 to 2 tesla. In addition, the present invention relates to cellular elastomers obtainable in this way, in particular motor vehicle helper springs, motor vehicle shock absorber bearings, motor vehicle chassis bearings comprising the cellular elastomers of the invention.
Cellular, for example microcellular, polyisocyanate polyaddition products, usually polyurethanes and/or polyisocyanurates which may if appropriate comprise urea structures and are obtainable by reaction of isocyanates with compounds which are reactive toward isocyanates, and processes for producing them are generally known.
A particular embodiment of these products is cellular, in particular microcellular, polyurethane elastomers which differ from conventional polyurethane foams in their significantly higher density of usually from 200 to 700 kg/m3, preferably from 300 to 700 kg/m3, their particular physical properties and the possible applications resulting therefrom. Such polyurethane elastomers are employed, for example, as vibration-absorbing and shock-absorbing elements, in particular in automobile construction. In automobiles, the spring elements produced from polyurethane elastomers are, for example, pushed onto the piston rod of the shock absorber in the overall shock-absorbing strut unit consisting of shock absorber, spiral spring and the elastomeric spring.
Cellular polyurethane elastomers can be produced only up to a particular material hardness since the material hardness is set only via the density. However, high hardnesses are absolutely necessary in wheel-conducting elastomer applications (bearings) in the area of suspension/chassis. A solution which allows an increase in hardness in one force direction (transverse to the vehicle) but leaves the other directions unchanged (soft) is therefore sought.
High hardnesses also have the disadvantage that hollow cylindrical helper springs based on polyurethane elastomers can no longer be removed from the mold over the core. A higher hardness, preferably only in the direction of force, would represent a solution here.
It was thus an object of the invention to develop cellular polyisocyanate polyaddition products, preferably cellular polyurethane elastomers, which solve the abovementioned problems and, in particular for wheel-conducting applications in a motor vehicle chassis, combine the advantages of a high material hardness and density with the advantages of the known polyurethane elastomers and their manufacturing techniques.
These objects were able to be achieved by the anisotropic cellular elastomers presented at the outset.